Two important chemical transmitters in brain are dopamine and serotonin. After being release from a neuron, the transmitter is later taken back up into by the cell via a protein called a transporter. Thus, the transporter plays an important role to modulate chemical transmission in brain. The dopamine transporter is the target site for the actions of cocaine and could, therefore, be called the "cocaine receptor." In addition, the dopamine transporter is a marker for the specific class of neurons that degenerate in Parkinson's disease. The serotonin transporter is the target for the new class of antidepressant medications such as Prozac. Over the past year, we have developed methods to image the dopamine and serotonin transporters in living brain using positron emission tomography (PET). Our work with imaging of these two transporters have included: 1) Drs. Higley (NIAAA) and Suomi (NICHD) have shown that monkeys who are reared without mothers tend to be shy, aggressive, and prone to alcoholism. Their data suggests that these abnormalities may be related to deficiencies of serotonin neurotransmission in brain. In collaboration with Drs. Suomi and Higley, we have begun studies to examine the levels of serotonin transporters (in comparison to dopamine transporters) in the brain of these animals. 2) We plan to perform imaging studies in human subjects with these two PET tracers to study several disorders, including depression, Parkinson's disease, Tourette's syndrome, and alcoholism. We have recently completed animal safety studies that are required before we initiate studies in human subjects, and such human studies will begin next year.